Lecture 12 - Ruminant Nutrition 2

Question 1

What are the major functions of calcium?

Answer 1

• Vital component of milk
• Actin-myosin coupling (muscle activity)
• Hormone and neurotransmitter release

Question 2

Calcium absorption in the body is largely facilitated by activated vitamin ___ and ___________ hormone

Answer 2

D; parathyroid

Question 3

What are three factors that can affect calcium absorption?

Answer 3

• Phosphorus and magnesium content
• High dietary zinc
• Oxalates

Question 4

True or False: Oxalates can be poisonous to ruminants, but the rumen can detoxify them up to a certain ingested amount

Answer 4

True

Question 5

What can occur when there are too many oxalates in the bloodstream?

Answer 5

They can form insoluble salts that will precipitate in the kidney and cause kidney failure

Question 6

True or False: Sheep are most susceptible to oxalate poisoning, followed by cattle, but livestock can develop a tolerance for oxalate-producing plants with gradual exposure in the diet

Answer 6

True

(Extra note: Gradual exposure to oxalates allows the rumen to build up a concentration of oxalate-degrading bacteria)

Question 7

How much soluble sodium oxalate does the Halogeton plant contain (on a dry matter basis)?

(Give the percentage range)

Answer 7

30 to 40%

Question 8

How do Rumex spp. plants cause hypocalcemia?

Answer 8

Oxalates bind calcium, which can lead to hypocalcemia if the plant is consumed in large amounts

Question 9

What percentage of extra-cellular calcium in the blood is ionized? Where is the rest of the calcium found?

Answer 9

• 55% ionized (the metabolically important calcium)
• 35% bound to albumin
• 10% bound to phosphate, citrate, HCO3-, and other ions

Question 10

True or False: Acid-base status influences albumin-to-calcium binding. For example, more calcium binds to albumin during acidosis, resulting in slightly lower Ca2+ in the blood and ECF

Answer 10

False; more calcium binds to albumin during ALKALOSIS

(The rest of the statement is true)

Question 11

Which metabolic abnormality often accompanies diseases that impair abomasal emptying, causing HCl to be trapped in the abomasum and forestomachs?

Answer 11

Metabolic alkalosis

Question 12

Why might acidosis trigger an increased release of calcium from the bone?

Answer 12

Less calcium binds to albumin during acidosis, so calcium may be released from the bone to act as a buffer and attempt to maintain calcium homeostasis

Question 13

What is the role of parathyroid hormone (PTH) in calcium regulation? Which cells release it?

Answer 13

• Increases Ca2+ in ECF back to the desired concentration (“normal range”)
• Promotes bone resorption to provide Ca2+ to the ECF
• Released by chief cells in the parathyroid

Question 14

PTH promotes a loss of _________ ion in the saliva and urine, resulting in an increase in ionized calcium and a decrease in ____________.

Answer 14

Phosphate; phosphorus

Question 15

Which hormone promotes the transformation of 25-hydroxyvitamin D to 1,25-hydroxyvitamin D (active form)?

Answer 15

PTH

Question 16

What is the function of calcitonin? Which cells release it and when?

Answer 16

• Promotes deposition of calcium INTO bone and calcium loss in urine to decrease Ca2+ in the ECF
• Released from thyroid C cells during hypercalcemia

Question 17

An acute flaccid paralysis that results from depleted serum calcium as it is lost into colostrum and milk

Answer 17

Milk fever

Question 18

When can periparturient hypocalcemia occur?

Answer 18

Before, during, or after calving (anytime around birth)

Question 19

Which stage of milk fever exhibits clinical signs such as standing, apprehensiveness, hypersensitivity, and tremors?

Answer 19

Stage 1

(Reflects loss of the dampening effect Ca2+ has on axonal sodium channels)

Question 20

Which stage of milk fever exhibits clinical signs such as recumbency, weakness (to degree of inability to stand), and head turning into flank (because too heavy to lift)?

Answer 20

Stage 2

(Continued loss of calcium influx at axonal motor end plate lowers ACh release per AP; also, less Ca2+ available in ECF to participate in muscular response to ACh)

Question 21

What occurs during stage 3 of milk fever?

Answer 21

Coma and death due to cardiac or respiratory failure; may regurgitate rumen contents and aspirate

Question 22

Why is it important to administer IV calcium solutions slowly?

Answer 22

Rapid infusion can lead to cardiac arrest (stone heart syndrome)

Question 23

When treating milk fever with calcium borogluconate, why will you likely see eructation, increased alertness, and a slower heart rate?

Answer 23

Muscle contractions will slow down but strengthen with a higher availability of calcium in the body

Question 24

What are two possible methods for preventing milk fever?

Answer 24

• Feed a diet low in calcium 1 month pre-partum to boost PTH and Vit D3 homeostasis early
• Feed anionic salts for 2 weeks pre-partum to induce mild metabolic acidosis

(Extra note: Do not forget to also supply adequate Mg2+ as it is a necessary cofactor for PTH release!!)

Question 25

What is the benefit of inducing a mild metabolic acidosis 2 weeks pre-partum?

Answer 25

Increases gut calcium absorption and bone utilization to maintain calcium homeostasis

Question 26

What is the primary role of Mg2+, and what does it compete with/inhibit?

Answer 26

Acts as a cofactor for multiple enzymes (including acetylcholinesterase) and for release of PTH from the parathyroid gland; competes with Ca2+

Question 27

True or False: Animals must consume Mg2+ in their diet, because Mg absorption from the GI tract is the only regulatory mechanism for ECF [Mg2+]

Answer 27

True - unlike calcium, Mg does not have specific hormones to regulate its ECF concentration, so it must come from the diet!

Question 28

What are considered good sources of dietary Mg?

Answer 28

Plant-based: legumes, nuts Animal-based: animal tissues, liver

Question 29

How is Mg absorbed in ruminants?

Answer 29

Across rumen wall via energy-dependent processes

Question 30

High nitrogen and K+ in a ruminant’s diet will _________ Mg absorption from the rumen

Answer 30

Reduce

Question 31

Metabolic disease of ruminants characterized by abnormally low ECF Mg2+ and calcium; affected animals exhibit uncontrolled/repetitive muscle contractions, hyper-irritability, and convulsions

Answer 31

Grass Tetany / Hypomagnesemic Tetany

Question 32

What does “early” vs “late” hypomagnesemic tetany look like in affected animals?

Answer 32

Early = muscle fasciculations, hyperesthesia, stiff gait, irritability/excessive alertness/nervousness Late = recumbency and convulsions; death may occur from respiratory or cardiac arrest

Question 33

Why are Mg salts often mixed with salt and grain when given as a dietary supplement?

Answer 33

They are not very palatable, so mixing with salt/grain helps to ensure consumption

Question 34

True or False: Plant uptake of Mg is not affected by the PO4(2-) content in the soil

Answer 34

False; Mg uptake is facilitated by adequate PO4(2-) in the soil

Question 35

A mineral that is a component of bone mineral and tooth enamel; 85% of total amount in the body lies in hydroxyapatite; dietary sources include grains, wheat bran, and supplements

Answer 35

Phosphorus

Question 36

____ calcium and _____ phosphorus in the blood triggers chronically elevated PTH, which can lead to a condition called “rubber jaw”

Answer 36

Low; high

Question 37

Where does phosphorus excretion primarily occur in the ruminant? What is the benefit of this?

Answer 37

In the gut via phosphorus being moved into saliva and lost into the GI tract; this process supples rumen bacteria with phosphorus (for ATP) and allows for phosphorus to be recycled into the blood, minimizing losses in urine

Question 38

A medical condition affecting ruminants on high-grain diets that is associated with the development of phosphate-based urinary calculi if urine becomes too highly concentrated

Answer 38

Urolithiasis

Question 39

Possible complication of milk fever with failure to respond to conventional therapy; affected cows are alert but show severe muscular weakness (may attempt to move by pushing partially up and moving around on their abdomen)

Answer 39

Hypophosphatemia

Question 40

How can the onset of lactation cause hypophosphatemia?

Answer 40

Lactation causes heavy calcium losses, triggering more PTH secretion, and PTH can move a lot more phosphate to the urine than usual

Question 41

What is the physiology behind hypophosphatemic rickets in young camelids?

Answer 41

Inadequate vitamin D leads to inadequate Ca and P absorption from the gut to mineralize bones (leading to micro-fractures which cause lameness and long bone deformities)

Question 42

True or False: In hypophosphatemic rickets, serum calcium may be completely normal even though phosphorus is noticeably reduced

Answer 42

True